Trying to create a grouped barchart in R - producing a stacked one instead

Question

I am trying to create a bar chart that has the number of each species grouped into years. I want each year represented on the x axis with the number of each of the 3 species grouped next to one another under each year.

I am working with the following dataset which contains year, species, and the number of species counted for that year.

structure(list(year = c(2018L, 2018L, 2018L, 2019L, 2019L, 2019L, 
2020L, 2020L, 2020L, 2021L, 2021L, 2021L, 2022L, 2022L, 2022L, 
2023L, 2023L, 2023L), species = c(1L, 2L, 3L, 1L, 2L, 3L, 1L, 
2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L), n = c(96L, 15L, 
126L, 84L, 8L, 109L, 87L, 20L, 71L, 116L, 13L, 157L, 108L, 10L, 
112L, 129L, 11L, 186L)), class = c("grouped_df", "tbl_df", "tbl", 
"data.frame"), row.names = c(NA, -18L), groups = structure(list(
    year = c(2018L, 2018L, 2018L, 2019L, 2019L, 2019L, 2020L, 
    2020L, 2020L, 2021L, 2021L, 2021L, 2022L, 2022L, 2022L, 2023L, 
    2023L, 2023L), species = c(1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 
    3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L), .rows = structure(list(
        1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 
        14L, 15L, 16L, 17L, 18L), ptype = integer(0), class = c("vctrs_list_of", 
    "vctrs_vctr", "list"))), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -18L), .drop = TRUE))

I tried the following however it produced a stacked bar chart instead of a grouped one. Also, for some reason the legend has species in a gradual shade rather than 3 distinct species.

barplot <- df2 %>% 
  ggplot(
    aes(x = year, y = n, fill = species))+
  geom_col(position = "dodge", width = 0.5, alpha = 0.5, color = "black", linewidth = 0.1)
plot(barplot)

Answer 1

As the variable mapped on fill is a numeric aka continuous variable you have to convert to a discrete or categorical variable using e.g. factor or explicitly map on the group aes:

library(ggplot2)

df2 |> 
  ggplot(
    aes(x = year, y = n, fill = factor(species))
  ) +
  geom_col(
    position = "dodge", width = 0.5, alpha = 0.5,
    color = "black", linewidth = 0.1
  )

df2 |> 
  ggplot(
    aes(x = year, y = n, fill = species, group = species)
  ) +
  geom_col(
    position = "dodge", width = 0.5, alpha = 0.5,
    color = "black", linewidth = 0.1
  )